Method for removing a fluorine compound(s) from gaseous mixture therewith

ABSTRACT

In a method for removing fluorine compound(s) from gaseous mixture therewith, the mixture is at first introduced to a gas scrubber of gas-liquid contacting type and then it is characterized in that the gas removed from the scrubber is introduced to a mist-catching means, said means comprising a porous filter medium in a film state having pores of a mean size of not more than 60 Mu and a nozzle or nozzles positioned above the surface of the medium, which can spray water or an aqueous alkaline solution on the surface of the filter medium into substantially the same direction as that of the stream of the gas, and liquid being sprayed continuously or intermittently. This invention is useful for removing a boron fluoride from gas.

United States Patent Tsukamoto et al.

[ Sept. 23, 1975 May 10, 1973 Foreign Application Priority Data Japan 48-51833 US. Cl. 55/71; 55/90; 55/94 lnt. Cl. BOID 50/00 Field of Search 55/71, 90, 93, 94, 233; 423/240, 293, 287; 261/94 References Cited UNITED STATES PATENTS Schytil et aI. 55/73 X Hynson et aI 261/94 X ALKALINE SOLUTION 3,445,182 5/l969 Tom-any... 261/94 3.492,789 2/I970 Jueng 55/94 [57] ABSTRACT In a method for removing fluorine compound(s) from gaseous mixture therewith, the mixture is at first introduced to a gas scrubber of gas-liquid contacting type and then it is characterized in that the gas removed from the scrubber is introduced to a mist-catching means, said means comprising a porous filter medium in a film state having pores of a mean size of not more than 60;}, and'a nozzle or nozzles positioned above the surface of the medium, which can spray water or an aqueous alkaline solution on the surface of the filter medium into substantially the same direction as that of the stream of the gas. and liquid being sprayed contin uously or intermittently. This invention is useful for removing a boron fluoride from gas.

11 Claims, 1 Drawing Figure IOJ WASTE- GAS SOLUTION V 8 WASHING LIQUID PURIFIED GAS I g I I0 :1"; 5 I

WASHING LIQUID US Patent Sept. 23,1975

m o cm I 53a @503 wzim METHOD FOR REMOVING A FLUOR'I'NE COMPOUND(S) FROM GASEOUS MIXTURE THEREWITH BACKGROUND OFT-HE INVENTION This invention relates to a method 'for removing a fluorine compound(s), particularly a boron fluoride from a waste gas containing the fluorine compound or compounds, such as hydrogen fluoride or boron fluorides.

Air pollution by a waste gas containing fluorineandlor fluorine compoundscauses a social problem, since plants, so processes using the compounds and processes forming fluorine compounds as byproducts should be carried out in closed loop system to prevent the leakage of the fluorine compounds out of the prov cesses. A variety of attempts have been made for at-" taining this object. I

In general, it is well known that since hydrogen flu'oride and boron fluoride are very water-soluble, a hydro gen fluoride corit aining waste gas is washed with water,

thereby removing hydrogen fluoride contained in the waste gas. "Fdr example, INDUSTRY AND ENGI NEERING cijigmrsirny v01. 46, No. 9,,pag1es 1769 f 1777 l'954) disclos'es that removal of hydrogen fluoride from a'hydrogen fluoride-containing 'wa stegas can be attained in hig li egfficiency by using aSarm fiber filter in a wet state as ari absorbing'bedQ l-lewever, this Process as e effc (for. removin 1 hydrogen fluoride from a mixture of hydrogen fluoride v and a largeamoun t of'a nfinert gas dil uent. v g

As mentioned, a boron fluoride yva tersolu bility like hydrogen fluoride. Therefore,it' is assumed that when a waste gas containing a boron fluoride is washed withwater, a boron'fluorid wouldbe easily ab sorbed by the water. v 7 i I Contrary: to expectation, fit, was found 7 that a boron fluoride is not efficiently absorbed water. That is, has been found that even when'a boron fluoride diluted with an inert gas such as air is washed with water by gas-liquid contact in a gas "scrubber: such ;asa pacl ed tower, a tower havingmu plates, a fluidized and the like, absorptionefficieneyfpf the boron fluoride .is very low, This fact w gu ld be realized: by the result'that the absorption 'e fficie ncy by'means, a gas scrubber i with a fluidized bed isin'g an aqueous hydrox; ide solution was measure gin' fan amount of more than 95%, forhydr tigen mange, whereas about 39% fora" boron fluoride.

tion efl'ieiencies we have 9a following fourfind as an affinity for water to bin is difficult to s i rm i'by an absorption medium, ;"(c) yv h en If m y a a H the absorption medium, mist is formed and (d) the mist drate. contacts ,with,

tends to fly with the waste gas from the absorption zone without being absorbed by the" treating solution. As a result, the absorption efficiency fora boron fluoride is poor. V 7

Making a variety' of attempts for increasing'the absorption efficiency for a boron fluoride on the basis of the above findings, we have found a methodfor efficiently absorbing a "boron fluoride. This invention forms the basis of this discovery.

Accordingly, it is an object of the invention to provide a method for efficiently'removi nga substantial amount of a fluorine 'compOundQs), particularly a boron fluoride, from a waste containing a fluorine compounds. M

it is a further object, of the invention to provide a method capable of absorbing a boron fluoride without flying such boron fluoride hyd rate mist with the gas.

Other objects of the invention will in part be obvious and will in part appear hereinafter. i I

I SUMMARY OF THE lNVENTlON This invention is in detail explained on the basis of. the following embodiment. 1

A fluorine .compound(s)-containing gas is passed through a gas scrubber of gas-liquid contacting type,

such asapacked tower, a tower having multi plates, a fluidized bed or the like tov perform a gas-liquid contact, thereby removing a portion. of the cpmpound(s) from the gas and thenthe gas so treated is passed through a mist-catching meansco rnprising a.po.-

rous filter medium in ,a..filmy state having pores with a mean size of not more than 60g anda nozzle or nozzles. positioned abovethe surface of, the filter medium,

cording to this invention, hydrogen fluoride and/or a boron fluoride is substantially removed from a waste gas containing thesame. i

DETAILED D imioN OFATHE INVENTION The inventors of this invention'have made an extended study of the kinds of raw-material, the forms and the mean size of filterpores most suitable for a filter 'in the filter in'edium"of this invention in order to catch fluorine "compound"(s)-containing mist, particularly a bor'on fluoride hydrate mist,"produced by passing a waste gas through agas scrubber described above.'

The filter riiedium'employed for carrying out the' method of this invention is a porous sheet material or a porous material in a fil'my state 'havin'gpores of 'a mean size of not more than 60 i; and a mean size of about 20 60y. being preferable, the range of about 20 40y. being most satisfactory it is preferable that the porous filter "medium is prepared by compressionsintering a powder comprising a i'aw material for the i filter medium. The size of the pores in the porous filter medium canbe adjusted by controlling the particle size of powder to be sintered, the pressure of compres- I sion molding and sintering conditions.

Since the mist to be treated is a boron fluoride and/or hydrogen fluoride, the raw material for the filter should be corrosion-resistant. Suitable materials include fluorine-containing resins, such as polytetrafluoro ethylene resin; polyolefin resins such as polyethylene or polypropylene, andpolyvinylidene chloride resin Polyethylene is preferred as the material. When a waste gas not containing hydrogen fluoride is treated, glassmay also be used as a material for filter.

A woven fabric, a non-woven fabric or a felt having a corrosion-resistance instead of the, porous filter medium used in the method of this invention is improper for use as a filter. The reasons are as follows:

The boron fluoride hydrate mist to be caught by the filter is a viscous liquid; and spraying of water or an alkaline aqueous solution is essentially required. Then, when a waste gas containing the mist is treated by passing it through the filter in the form of the fabric or felt described above, the mist and water or the aqueous solution clogs some of the gas-passing pores present in the filter, thereby resulting in increasing the resistance to passage of the gas through the filter. Simultaneously, the increase of the resistance to passage of the gas causes expansion of the non-clogged pores remaining in the filter and make the gas pass only through the pores, thereby giving rise to a localized flow of the gas. Therefore, in a case using a filter in the form of the fabric or felt, not only pressure loss results from the reduction of the number of effective pores, but also efficiency of holding the-mist is loweredbecause of the expan'sion of the gas-passing'pores. Y 1

O nthe other hand; the porous filter medium men surface of the -porous filter medium for catchingthe,

mist should. be continuously or intermittently washed with water-while the gas is passingthrou'gh the filter. Washing is particularly effective for catching the boron fluoride-containing mist, because blockage of the pores resulting from viscousness of boron fluoride hydrate is prevented by the washing. The amount of water used depends on the proportion of the fluorine compounds contained in the waste gas, the amount of waste gas passed, the mean size of the pores and the distribution of water droplets on the surface of the filter. It may be enough to say that the lower limit of the amount is to remove the mist held by or absorbed in the pores. The higher limitof the amount is decided from the economic viewpoint. I I

The particular amount of water used is more than about 0.1, preferably 1 to 5 mole, per a mole of a boron fluoride hydrate contained in the waste gas treated.

Though the waste gas may contain a small amount of solids with the mist according to circumstances, such solids can be easily removed from the pores by using treating solutions other than water, wherebyblockage of the filter by the solids can be prevented. To the best of our knowledge from such facts, spraying of water or an aqueous alkaline solution on the filter as in this in- Y sprayed on the surface of the filter medium into substantially the same direction as that of the stream of the gas. i

Both the gas and water or the alkaline solution are passed asstreams from the upper portion of the mistcatching means to the lower portion thereof. That is, the stream of the gas is not in countercurrent relation withthat of the liquid. p In order to uniformly. distribute water over the surface of filter forproduction on commercial basis, it is preferable to spray the water or the solution in a state of fog on the surface from nozzle(s-).

- In the practice of this invention, an absorbing medium used in the mist-catching means may be water or an aqueous alkaline solution, such as an aqueous solution of a hydroxide or carbonate of alkali metal or alkali earth metal. v

.ln operating the mist-catch means employed in this invention, the inside temperature of the means is not critical. Generally speakingQthe inside temperature of the means is desired to be low, due to the reasons that a fluorine compound, particularly a boron fluoride hy- 'invention. In FIG. 1, line 1 for introducing a waste gas to be treated, line 2 for introducing water or an aqueous alkalineso'lu tion, gas scrubber 3, line4 for withdrawing the gas so treated from scrubber 3 and introducing it to mist-catching means 5, porous filter medium 6, nozzle 7 for. spraying water or an aqueous alkaline solution, line 8 for introducing water or the solution to means 5, line 9 for withdrawing the treatedgas and line '10 for withdrawing the washing solution from means 5 are shown.

A portion of the fluorine compounds contained the I waste gas is removed from the gas in gas scrubber 3 by gas-liquid contact and then the gas so treated is fed through line 4 from scrubber 3 to means 5. in means 5, a substantial amount of fluorine compound s), particularly a'boron fluoride hydrate contained in the waste gas is removed from the gas by passing the gas through filter medium 6. The fluorine compound(s) mist which is absorbed in the pores the filter is washed with water or' the alkaline solution. I

in the mist-catching means as explained above, the filter medium is 'producedby shaping a porous filter sheet into a cylinder. The diameter andlength of the cylinder, andthe number of the cylinders are selected so that a desired filter surface area may be obtained.

' Furthermore, the'length of the cylinder may be determined by the spraying effect of the liquid. The diameter of the cylinder may be determined by the thickness of the filter sheet and strength thereof. The number of the cylinders may be decided on the basis of the dispersing state of gas to be treated and the ability of spray 7'for spraying liquid. The cylindefls) is so arranged as to be positioned vertically in means 5. Means 5 may be designed so that the gas to be treated is passed through the filter from the outside surface of the cylinder to the inside thereof, while water or an aqueous alkaline solu- 6 a mixture of hydrogen fluoride with a large volume of an inert g as. Of course, the present invention is also useful for treating a waste gas containing a boron fluoride and hydrogen fluoride.v

tion in a fog state is sprayed on the surface of the filter 5 Therefore; this invention can substantially. prevent lhto suhstahtlahy the Same direction as that Of the air-pollution. Significance of this invention for industry stream of the gas. The wash water or the alkaline solui great is Stored in the bottom Outside the Vertieahy P The invention is further illustrated, but in no way limtioned cylinder(s). The form of the filter medium may i d b the following examples. be a square pillar or a plate. A cylindrical form is pre- I the following examples, a fluorine fraction was ferredmeasured on the basis of Analytical method for deteris preferable to Introduce the g to the mistmination of fluorine compounds in exhaust gas" decatching means through the inlet for gas positiml d scribed in HS (Japanese Industrial Standard) K 010.5. above the filter medium, while continuously or Jit er-r mittently spraying on the surface ,oflthe medium water y I EXAMPLE I or the aqueous alkaline solution from 1 a nozzle posi- I h fl w h t of FIG. I, a boron triflu'oride gas ditioned above the filter medium luted w ithtair was fed to gas scrubber 3 comprising a when some po i the medium eh theme. packed tower through line 1, and an aqueous alkaline Sure g .b c m si fi h solution was fed to scrubber 3 through line 2. The gas can not P gh the m lh- In -t e was allowed to contact with the solution by countercurthis PtQblem, for e mp the de r eqf the rent system in gas scrubber 3. The gas so treated was ans 51 is in e hrougl1rd ti n f t hwithdrawn from scrubber 3 through line 4 and fed to Side 's p y y elevatingv l lQfWQ F-Q h mist-catching means 5 Porous filter medium 61in a cytioh Stored its ot By hl 'i "be e e lindrical form made from polyethylene was arrangedfin I ble to make the gas pass through the rnedi um,.thepres- 2 means 5. The filter has pores of a mean size of Qab out sure loss mentioned above notwithstanding In general, 20 p" The washing solution was sprayed from 110':- the inside pressure of the closed means may selected zle 7 mounted on the top of means k i from a superpressuretof less thanZQ kglcm gauge. The effect of washing boron "ride-containing Alternatively, the pressure lossmay be pompensated gas was determined by measuring fluoride fractions for by maintaining theoutlet for gaspf the cylindrical contained in the treated waste gas withdrawn fromline filter at a reduced pressure, that is, by the gas 9. The results are shown in Table 1. In Table 1, the flufrom the outle t for gas of the means. In this case the inorine fractions .cpntainedin "the gas were calculated in side pressure of the means 5 may b kept at a red ee mg F7N lh Tablel. It linear concentration concentration it velocity of fluorine 7.- 1 of fluorine amount of gas k fraction fraction of gas based upon contained contained passed the unit in the gas int-he gas t through areaof the at the inlet at the outlet. absorption filter surface of of means 5 ofineans 5 cfficiency 1 the'filter 1 (Nm lhr) mediumhnlmin) (mgF /N m") (mgFf/N m") F1 1 .2 "1.0 i 483 3.07 99.36 L8 1.5 490 t 2.90 99.40. 2.8 2.0 48,3 3.8 99.21 1.2 1.0 32.9 0. 2; 97.93 ,,-..1.8 1.5 33.1 1:12 96.62 2.4 2.0 52.5 0,159 q 97.26

r F1. "Id e '1 =11 if U. pressure select dfr a reduced pressu of more than EXAMPLE 2- 200 mmHg, during the time when the gas is sucked .4 g g from the meahs- A The process of Example '1 was repeated withawaste AS eXPIdmed above, the Presentmvehhoh Very gas containing equimolar amounts of each of boron triful for treatlng. a waste gas contfumng fluormt: fluoride and hydrogen fluoride with air diluent except pounds particularly a heron fluoride which can h that the treatment in means 5 was carried out at a reremoved by a conventional gas scrubber of gas-liquid bl h contacting type, because of formation of a boron fluoduced h f by usmg a (not 8 own conride hydrate mist. This invention is also useful for reheeted Wlth hhe 9 and the mean SlZe of the Pores was moving hydrogen fluoride from a waste gas comprising about 40 50y. The results are shown in Table 2.

Table 2 linear concentration concentration velocity of fluorine of fluorine amount of gas fraction fraction of gas based upon contained contained passed the unit in the gas in the gas through area of the at the inlet at the outlet absorption filter surface of of means 5 of means 5 efficiency the filter (Nm lhr) medium (mg F/N m" (m/min) mg FlN m I Table 2 Continued linear concentration concentration velocity of fluorine of fluorine amount of gas fraction fraction of gas based upon contained contained passed the unit in the gas in the gas through area of the at the inlet at the outlet absorption filter surface of of means of means 5 effieieney the filter (Nm lhr) medium (mg F /N 'm" (/1) in) m F'lN m") EXAMPLE 3 l5 3. The method defined in claim 1, wherein'the porous The apparatus employed was the same as in Example filter medium has pores of a mean size of about 40 l, but was so large as to enable the treatment of 750 N [ha/ht f gas which contained 250 mg f the 4. The method defined in claim I, wherein the aquecombined amount of a boron fluoride and hydrogen alkaline 0 an aqueous solution of a yfl id as a total fl i f tio 20 droxide or a carbonate of an alkali metal or an alkaline An aqueous alkaline solution was used as a gasearth metal. absorbing medium to fix a portion of the fluorine com- 5- The method defined in claim 1, wherein the filter pound. At least two porous filter mediums made from in the porous filter medium is a porous filmy material polyethylene in a cylindrical from, and having pores prepared by compressionsintering fP co p iswith a mean size of about 30 40p. were arranged'in ing a raw material selected from the group consisting means S'sdthat the filter area was 8 square meters. The of fluorine-containing resins, polyolefin resins, polyvisolution used was sprayed on the filter at the rate of 0.5 nylidene chloride resin and glass. m /hr. The total fluorine fraction contained in the gas 7 6. The method defined in claim '1, wherein the filter withdrawn from the mist-catch means was 0.7 mg F'lN i a polyethylene 'filter.

m". H i 7. The method defined in claim 1, wherein the filter wh is claimed v a in the porous filter medium is cylindrical.

Avmethvd for m v fluoride compounds m- 8; The method defined in claim 1, wherein in the prising hydrogen fluonde' and fluonde" from mist-catching means one or more inlets forthe gaseous gaseous f f cmammg the same chractenzed by mixture removed from the gas scrubber is positioned introducing said gaseous mixture to a gas scrubber of 5 abovg the filter medium gas-liquid contacting type, thereby removing from the 9A The method defined in claim 1, wherein the mist gaseous f Porno of the fluonde compfmnds' catching means is so operated that the inside pressure and then delivering the so treated gaseous mixture, pf the means is a shperpressure of less them 20 kg per which contains fluoride compounds substantially com- 40 Square centimeter gauge P fluonde l f m form to l v 10. The method defined in claim I, wherein the mistcatchmg means c.ompnsmg a pmous filter pedmm m catching means is so operated that the inside pressure a filmy state having of a i g E of themeans is kept at a reduced pressure of more than than 60 one or m es posmon? a l 200 mmHg. during the time when the gas is sucked the surface of the medium, continuously or mtermrtl t ous alkaline solution from said means' tent Spraying wa er or an aqiie -I1. The method defined in claim I, wherein an on the surface of the filter medium in substantially the i amount of water or an aqueous alkaline solut on same direction as that of the treated gaseous mixture,

sprayed on the surface of the filter medium IS more thereby removing a substantial amount of boron fluo- I than 0.1 mole per mole of a fluoride hydrate contained nde 1n the form of a hydrate from said gaseous mixture. the aseous mixiure removed from is Scrubber 2. The method defined in claim 1, wherein the Porous g g filter medium has pores of a mean size of about. 20 1.1..

UNITED STATES PATENT AND TRADEMARK OFFICE CETIFICATE OF CORRECTION S PATENT NO. I 3,907,522

DATED September 23, 1975 INVENTOR(S) I YOUJI TSUKAMOTO et al It is certified that error appears in the aboveidentitied patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 38: replace "Saran" with SARAN Column 6, Table 2, second column heading, last two lines: 8

delete "mg F /N m Column 6, Table 2, fourth column heading, last line:

delete and insert (mg F'/N m 9 Column 6, Table 2, fifth column heading, last line:

5 insert Column 7, Table 2 continuation, second, fourth and fifth column headings, same as 2), 3) and 4).

Signed and Scaled thisi thirtieth D f March 1976 5 [SEAL] Arrest.-

RUTH C. MASON C. MARSHALL DANN Q Arresting Officer Commissioner ufParenrs and Trademarks g i 

1. A METHOD FOR REMOVING FLUORIDE COMPOUNDS COMPRISING HYDROGEN FLUORIDE AND BORON FLUORIDE FROM A GASEOUS MIXTURE CONTAINING THE SAME, CHRACTERIZED BY INTRODUCING SAID GASEOUS MIXTURE TO A GAS SCRUBBER OF GAS-LIQUID CONTACTING TYPE, THEREBY REMOVING FROM THE GASEOUS MIXTURE A PORTION OF THE FLUORIDE COMPOUNDS, AND THAN DELIVERING THE SO TREATED GASEOUS MIXTURE, WHICH CONTAINS FLUORIDE COMPOUNDS SUBSTANTIALLY COMPRISING BORON FLUORIDE HYDRATE IN MIST FORM, TO A MISTCATCHING MEANS COMPRISING A POROUS FILTER MEDIUM IN A FILMY STATE HAVING PORES OF A MEAN SIZE OF NOT MORE THAN 60U AND ONE OR MORE NOZZLES POSITIONED ABOVE THE SURFACE OF THE MEDIUM, CONTINUOUSLY OR INTERMITTENTLY SPRAYING WATER OR AN AQUEOUS ALKALINE SOLUTION ON THE SURFACE OF THE FILTER MEDIUM IN SUBSTANTIALLY THE SAME DIRECTION AS THAT OF THE TREATED GASEOUS MIXTURE, THEREBY REMOVING A SUBSTANTIAL AMOUNT OF BORON FLUORIDE IN THE FORM OF A HYDRATE FROM SAID GASEOUS MIXTURES.
 2. The method defined in claim 1, wherein the porous filter medium has pores of a mean size of about 20 - 60 Mu .
 3. The method defined in claim 1, wherein the porous filter medium has pores of a mean size of about 20 - 40 Mu .
 4. The method defined in claim 1, wherein the aqueous alkaline solution is an aqueous solution of a hydroxide or a carbonate of an alkali metal or an alkaline earth metal.
 5. The method defined in claim 1, wherein the filter in the porous filter medium is a porous filmy material prepared by compressionsintering of powders comprising a raw material selected from the group consisting of fluorine-containing resins, polyolefin resins, polyvinylidene chloride resin and glass.
 6. The method defined in claim 1, wherein the filter is a polyethylene filter.
 7. The method defined in claim 1, wherein the filter in the porous filter medium is cylindrical.
 8. The method defined in claim 1, wherein in the mist-catching means one or more inlets for the gaseous mixture removed from the gas scrubber is positioned above the filter medium.
 9. The method defined in claim 1, wherein the mist-catching means is so operated that the inside pressure of the means is a superpressure of less than 20 kg. per square centimeter gauge.
 10. The method defined in claim 1, wherein the mist-catching means is so operated that the inside pressure of the means is kept at a reduced pressure of more than 200 mmHg. during the time when the gas is sucked from said means.
 11. The method defined in claim 1, wherein an amount of water or aN aqueous alkaline solution sprayed on the surface of the filter medium is more than 0.1 mole per mole of a fluoride hydrate contained in the gaseous mixture removed from the gas scrubber. 